Transmission of light variations by frequency variations



April 7, 1 936.

J. H. HAMMOND, JR 2,036,869

TRANSMISSION OF LIGHT VARIATIONS BY FREQUENCY VARIATIONS Filed May 18, 1929 I VVIv m WA INVENTOR JOHN HAYS HAMMOND 'JR- ATTORNEY Patented Apr. 7, 1936 TENT OFFICE TRANSMISSION OF LIGHT FREQUENCY V w tond, Jan, Gloucester, t

VARIATIONS BY TIONS Application May 18, 1929, Serial No. 364,107

exist between it and the modulation at the transmitter and no possible method has been devised whereby the receiver mechanism may differentiate between the amplitude variations at the transmitter and those caused by the phenomena in the intermediatemedia.

It is an object of this invention to provide a system of transmission of varying light and sound intensities whereby this drawback in the systems at present in use may be overcome.

It is a further object of this invention to provide a system of radio transmission and reception whereby signals may be sent for signal purposes with' freedom from fading.

It is a still further object of this invention to provide a transmitting and receiving system wherebydifierent variations of light intensities may be sent from onepoint to another in sequence, of high speed, with freedom from distor-- tion due to the fading.

It is a further object of this'invention to provide a system of transmission of light sequences having a definite correspondence between the intensity of the light received and the light intensity at the sending station.

These and other objects will become apparent from the following specification taken in connection with the appended drawing.

In carrying out my present invention for example, the frequency of 3,000 kc. may be made to correspond to no light, 3,001 kc. may be made to correspond to a weak light, 3,002 kc. may be made to correspond to a medium light; 3,003 kc.

to a strong light, and 3,004 kc. to an intense light I These radiations of light sequences may be used.

in constructing a picture for photographic reproduction corresponding to a picture at a transmitter. v

Having thus briefly outlined the features embodied and underlying my invention, attention is invited to the accompanying drawing in which:

Fig. 1 is a transmitter adapted to convert vary- (iCil. 178-7) ing light intensities into varying frequency radio tracii'ismission in accordance with my invention; an

Fig. 2 is a receiver for cooperation with the transmitter of Fig. 1 for the conversion of the varying frequencies received, into the corresponding varying lightintensities.

Attention is now more particularly called to Fig. 1. This figure shows a soin'ce of light i which is of a varying-intensity, controlled, as for instance by a picture to be transmitted, and which is focused by the lens 2 upon a photoelectrio cell 3. This cell, in circuit with the resistor d and the battery 5, produces a voltage across the grid to filament of tube 6 in a well known manner, which voltage corresponds to the variations in light intensity. This voltage is indirectly amplified by causing it to modulate an auxiliary frequency circuit. The tube 6 operates as a modulator with the photoelectric voltage impressed on the grid and a continuous frequency voltage of suitable high frequency impressed in series with the plate from the source I. By the mixing action through the plate impedance 0, a modulated voltage is produced, and transferred by means of a condenser 9 to the amplifier-device I0 in a well known manner. After suflicient amplification by the tube l0 or by means of further amplifiers as necessary, the modulated auxiliary currents are impressed through the condenser ll upon the grid of the tube i2. The grid of the tube i2 is so biased by a suitable battery that it will draw little plate current when the light source 0 is at minimum. This tube I 2 operates as a demodulator. The auxiliary frequency existing in the plate circuit is bypassed by the condenser i3, leaving a current flowing in the direction indicated by the arrows which rises and falls in intensity in accordance with the strength or weakness of the light of the source I. This current passes through a series of magnet windings i5, I6, I! and I8, which control the armatures I9, 20, 2|, and 22, respectively. The air gaps of these devices are so adjusted that the armature IQ for instance, will be attracted on a slight plate current and armature 22 only on an intense increase of plate current. The intermediate armatures 20 and 2! are so adjusted that they will be attracted to the electromagnets by current intensities intermediate of those required to operate armatures i9 and 22. These armatures are connected to condenser plates which cooperate with a common condenser plate to fonn the condensers 23, 2t, 25, and 26. The condensers 23, 2t, 25, and 26, thus forming a variable step-by-step condenser, are adapted to supplement the condenser 21 and the inductance 28 determining the frequency of the oscillations of the radio oscillator 23. Normally, this oscillator may generate, for example, a current of the frequency of 3,000 kc. but upon opening of the circuits of condensers 23, 24, 25, and 23, in turn, this frequency increases by steps of 1,000 cycles to the value of 3,004 kc. Thus the frequency of energy emitted from the radiator or antenna 30 is controlled with exact and definite correspondence of the frequency with the intensity of the light source I.

Referring now more particularly to Fig. 2, there is shown a receiver for cooperation with the transmitter shown in: Fig. 1. This receiver includes a receiving and tuning system 3! and is provided with a local oscillator 32 for stepping down the received radio continuous wave into a low frequency constant amplitude current. For combining the locally produced and received oscillations, the detector 33 is provided and for amplifying the resultant low frequency there is provided an amplifier 34.

,The plate circuit of the amplifier 34 contains a series of inductances which are coupled to tuned grid circuits, 35, 85, 31, and 38 which are tuned to the intermediate frequencies which will be produced by the combination of the frequency generated by the oscillator 32 and the incoming varying frequencies. Each of these tuned circuits are connected to the grid of an amplifier device. The circuit 38, for example, is connected to the grid of the amplifier device 42, which grid is so biased that it will act as a detector so that a uni-directional current will exist in the output coil 46. Each of the other detector amplifier devices are connected with a similar output coil 43, 45, and 46, and each of the'output coils constitutes the armature magnets of a relay 41, 48, 49, and 50.

For reproducing. the varying light which has been used to control the current in the photoelectric cell 3 of Fig. 1, a light 5| is used. This light is adapted to be supplied by the alternating source 52 through the transformer 53. The amount of current flowing through said light is regulated by means of the resistance composed of the sections 54, 55, 56, and 51. The relay contacts 41, 48, 48 and- 50 are adapted to cut out various portions of the resistance to permit the light to be operated through the entire resistance or any number of the sections. Thus, for instance, when the relays are all open the current will pass through the entire resistance whereas if the relay contacts 41, 48, 48, and 50 are closed in sequence the resistance in the circuit will be cut down by the amount of the resistance of sections 54, 55, 55, and 51 in succession respectively. The light 5| may be utilized in the usual and well known manner in reproducing a facsimile etc. I

Having thus described my invention, I will now describe its operation.

Assuming that there is no light at the source I, there will be minimum modulation of the frequency produced by the oscillator 1 and consequently all of the condensers 23, 24, 25, and 25 will be supplementary to the condenser 21 and the impedance 28 in determining the frequency of the generator 28. This would cause the generator 29 to produce and radiate the lowest of the frequencies which it is arranged to transmit, or, in other words, 3,000 kc. However, upon increase in the light intensity the condensers 23,

24,25 andflwouldbeopenedinturn'endthe frequency oiLths generator 23 which would be transmitted by the antenna 38 would be increased by steps of Ike. upon the opening of each of the condensers up to the value of 3,004 kc.

with the above stated transmitter frequencies, the local oscillator may be set to produce 2,995 kc. so that the resulting low frequency current would be of from 5 to 9 kc. depending on whetha' the signal intensity or the light intensity at the transmitter is no light, weak, medium, strong or intense. The low frequency produced by the detector 33, and existing in its plate circuit, is amplified by the tube 34 and existing on the plate circuit of tube 34 operates the selective relays. .With minimum light intensity at the transmitter and a consequent transmission of 30 kc. the heterodyne receiver would produce an intermediate frequency of 5 kc. which would be improper to operate any of the relays of Fig. 2 and consequently the entire resistance would be in series with the light source 5i and its energy source 52 and the light 5i would be minimum.

As the frequency of the transmitter varies through that produced by intermediate light in tensities there would be produced at the receiver intermediate frequencies of 6, '7, 8, and 9 kc. in succession which would selectively excite the relays 41, 48, 48 and 50 likewise in the same succession and increase the intensity of the light source 5! by a corresponding amount as these relays remove the varying combinations of re-' sistances from its circuit. With a strong light at the transmitter and 9 kc. current in the plate circuit of the amplifier tube 34, the circuit 38 which is tuned to 9 kc. responds and actuates the grid circuit of the tube 42. This serves to close the contact 50 and thus decreases the resistance in the circuit of the light 5| to the minimum amount. Similarly, a 6 kc. current would close the contact 41; 1 kc. would close the contact 48; and 8 kc. would close the contact 48.

Having thus described my invention, it is to be understood that I am not to be limited to the'specific form and embodiment shown and described for the purpose of illustration only, but by the scope of my invention as set ,forth in the appended claims.

I claim:

1. Means for the transmission of varying light intensities by frequency variations which comprises, a transmitter including a photoelectric cell, the resistance of which is adapted to be varied by the light variations it is desired to transmit, a source of intermediate frequency, means for modulating said intermediate frequency in accordance with the fluctuation produced in a circuit by the varying resistance of said photoelectric cell, means for amplifying the modulated intermediate frequency, means for detecting the intermediate frequency and producing a uni-directional pulsating current the intensity of which will vary inversely with the resistance of the photoelectric cell, a circuit for said unidirectional current, a plurality of relay means in said uni-directional current circuit, each of which relay means is adapted-to be operated by a progressively increasing amount of current, a generator of high frequency energy to betransmitted, means for controlling the frequency of such energy including a plurality of condensers, each of which is adapted to be controlled by one of the above mentioned relays so that as the unidirectional current above referred to increases an increasing number of condensers are removed from the frequency controlling circuit of the high frequency generator and the frequency of high frequency oscillations will thus be increased step by step with the decrease in resistance corresponding to an increase in light intensity, and means for transmitting the high frequency energy thus varied, and a receiver forthe varying high frequency energy which comprises, an input circuit adapted to receive all of the frequencies transmitted by the transmitter with practically equal intensity, a high frequency generating means for heterodyning with the incoming frequencies, 'a modulator for combining the incoming frequencies and the locally produced frequency, means for detecting the heterodyne frequencies, selectively tuned means associated with the output of said detecting means consisting of a plurality of tuned circuits adapted to respond to the various heterodyne frequencies produced by said combining, means for independently amplifying the several heterodyne frequencies produced as they are selectively picked up by said selective circuit, relay means associated with the output of each of said amplifier means, a light device, a source of energy for said device, a tapped resistance included in the circuit between said light device and the source of energy therefor, and connections whereby said relays are adapted to bypass different portions of said tapped resistance whereby the intensity of the light may be varied in accordance with the heterodyne frequency and consequently in accordance with the frequency of the current received and the original light intensity.

2. Means for the transmission of varying light intensities by frequency variations which comprises, a transmitter including a photoelectric cell, a source of intermediate frequency, means for modulating said intermediate frequency in accordance with the varying resistance of said photoelectric cell, means for amplifying the modulated intermediate frequency, means for detecting the intermediate frequency and producing a uni-directional pulsating current a plurality of relay meansin said uni-directional current circuit, each of which relay means is adapted to be operated by a progressively increasing amount of current, a generator of high frequency energy, means for controlling the frequency of said en- 'ergy including a plurality of condensers, each of lay means associated with the output of each of said amplifier means, a light device, a source of energy for said device, a tapped resistance included in the circuit between said light device and the source of energy therefor, and connections whereby said relays are adapted to by-pass different portions of said tapped resistance whereby the intensity of the light may be varied in accordance with the original light intensity.

3. Means for the transmission of varying light intensities by frequency variations which includes. a transmitter including a photoelectric cell, a source of intermediate frequency, means for modulating said intermediate frequency in accordance with the varying resistance of said photoelectric cell, means for amplifying the modulated intermediate frequency, means for detecting the intermediate frequency and producing a unidirectional pulsating current, a plurality of relay means in said uni-directional current circuit, each of which relay means is adapted to be operated by a progressively increasing amount of current, a generator of high frequency energy to be transmitted, means for controlling the frequency of said energy including a plurality of condensers, each of which is adapted to be controlled by meet the above mentioned relays, and means for transmitting the high frequency energy thus varied.

4. In a system for the transmission of varying light intensities by frequency variations of the carrier energy, a receiver which comprises, an input circuit adapted to receive with practically equal intensity all the components of the varying frequency carrier wave transmitted by the transmitter, a high frequency generating means, a modulator for combining the incoming varying frequency carrier and the locally produced frequency, means for detecting the heterodyne frequencies, selectively tuned means associated with the output of said detecting means, means for independently amplifying the several heterodyne frequencies produced, relay means associated with the output of each of said amplifier means, a light device, a source of energy for said device, a tapped resistance included in the circuit between said light device and the source of energy therefor, and connections whereby said relays are adapted to bypass diiferent portions of said resistance whereby the intensity of the light may be varied in accordance with the original light intensity.

5. Means for the transmission of varying light intensities by frequency variationswhich includes,

\ amount of said pulsating current, a generator of the high frequency energy to be transmitted, means for controlling the frequency of said energy by the above mentioned relays so that the frequency of the high frequency oscillations will be increased step by step corresponding to an increase in light intensity, and means for transmitting the high frequency energy thus varied, and a receiver for the varying high frequency energy including, an input circuit, selectively tuned means associated with the input circuit and adapted to respond to the various frequencies received, means for independently amplifying each of the several frequencies relay means associated with the output of each of said amplifier means, a light device, and means whereby the intensity of the light may be varied by said relays in'accordance with the frequency of the current received and therefore the original light intensity.

6. Means for the transmission of varying light intensities by frequency variations, which includes, a transmitter including a photoelectric cell, means for producing a uni-directional pulsating current the intensity of which will vary inversely with the resistance of the photoelectric cell, a plurality of relay means each of which relay means is adapted to be operated by a progressively increasing amount of said pulsating current, a generator of the high frequency energy to be transmitted, means for controlling the frequency of said energy by the above mentioned relays so that the frequency of the high frequency oscillations will be increased step by step corresponding to an increase in light intensity, and means for transmitting the high frequency energy 'thus varied.

7. Means for the transmission of varying light intensities by frequency variations which comprises a transmitter including a light sensitive device, relay means controlled by said light sensitive device, a generator of the carrier frequency energy to be transmitted, means for controlling the frequency of said energy by the above mentioned relay means so that the frequency of the carrier frequency oscillations will be varied in accordance with changes in the light intensities a,ose,sea

and means for transmitting the carrier frequency energy thus varied.

8. Means for the transmission of varying light intensities by frequency variations which includes a transmitter including a light sensitive device, an electrical circuit, means for producing a flow of current through said circuit, means including the light sensitive device for controlling the intensity of flow of the current through said circuit, a plurality of relay means, each of which relay means is adapted to be operated by a progressively varying amount of said current, a carrier frequency generator, means for controlling the frequency of the energy generated by the carrier frequency generator by the above mentioned relay means so that the frequency of the carrier frequency oscillations will be varied step by step corresponding to variations in light intensity, and means for transmitting the carrier frequency energy thus varied.

JOHN HAYS HAMMOND, Jr. 

